This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-04-13
177. Lvalues vs rvalues in copy-initializationSection: 9.5 [dcl.init] Status: CD1 Submitter: Steve Adamczyk Date: 25 October 1999[Moved to DR at 4/02 meeting.]
Is the temporary created during copy-initialization of a class object treated as an lvalue or an rvalue? That is, is the following example well-formed or not?
struct B { };
struct A {
A(A&); // not const
A(const B&);
};
B b;
A a = b;
According to 9.5 [dcl.init] paragraph 14, the initialization of a is performed in two steps. First, a temporary of type A is created using A::A(const B&). Second, the resulting temporary is used to direct-initialize a using A::A(A&).
The second step requires binding a reference to non-const to the temporary resulting from the first step. However, 9.5.4 [dcl.init.ref] paragraph 5 requires that such a reference be bound only to lvalues.
It is not clear from 7.2.1 [basic.lval] whether the temporary created in the process of copy-initialization should be treated as an lvalue or an rvalue. If it is an lvalue, the example is well-formed, otherwise it is ill-formed.
Proposed resolution (04/01):
In 9.5 [dcl.init] paragraph 14, insert the following after "the call initializes a temporary of the destination type":
The temporary is an rvalue.
In 14.2 [except.throw] paragraph 3, replace
The temporary is used to initialize the variable...
with
The temporary is an lvalue and is used to initialize the variable...
(See also issue 84.)
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